Rat Infestation Poses a Threat to Coral Reefs in Oceanic Islands

A new study was published in the journal Nature that reveals a research on the islands in the Chagos Archipelago in the Indian Ocean. It appears that islands that are infested with rats have only two birds per hectare compared to the rat-free islands, where the number of birds is significantly higher, reaching an average of 1,243 birds per hectare.

More bird droppings, more thriving coral reefs

According to Nick Graham, who is one of the study’s researchers, the islands that have no rodents seem to have much healthier coral reef ecosystems. The team of researchers, comprising Graham and his colleagues, believes that this is due to the nutrients provided by bird excrement to the coral reefs.

Because the bird droppings contain large amounts of nitrogen, they are extremely useful for the reefs, keeping them healthy. In order to determine which islands are better for the coral reefs to thrive, the researchers run some tests for nitrogen isotopes on 12 islands, as well as in close by reefs. Half of these islands were infested with rats, while the other half was not.

Nitrogen-rich guano from birds reaches the coral reefs

In the soil of the islands where there were no rats, larger amounts of heavy nitrogen were found, as the number of birds in these places was quite high. The same quantity of nitrogen was found in the algae, sponges and in the fish from the coral reefs that surround the rat-free islands.

Based on these findings, it looks like the guano from birds, which contains a lot of nutrients, can travel from the islands into the sea and therefore into the nearby corals. Another discovery made by the researchers was that the fish neighbouring the islands without rodents were in abundance. Overall, in Graham’s opinion, rat eradication would definitely bring benefits to the ecosystems and would increase coral reef productivity. Rat control must be taken into consideration as a conservation priority to preserve coral reefs.